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Wednesday, November 10, 2010

The World Is Full of Rare Snakes

Recently, media
outlets have been reporting the story of the Antiguan Racer, Alsophis
antiguae. Unfortunately, they have been hyping it as the "World's
Rarest Snake." Alsophis antiguae is small species with an
interesting sexual dimorphism, females are much larger than males and silvery-gray
with blotches and stripes, while the smaller males are dark brown with creamy
blotches. The species was distributed throughout Antigua and Barbuda, in the
West Indies, but in 1926 H. W. Parker declared the species extinct. However,
Rick Sajdak and Robert Henderson rediscovered it in 1991 on Great Bird Island off
the northeast coast of Antigua. In 1995, Jenny Daltry and colleagues estimated
the population at 51 snakes and found the Black Rat was decimating the
population. The Jersey Zoo attempted a captive breeding program in 1996 that
was unsuccessful. In 1999, ten specimens were moved to Rabbit Island where the
Black Rat had been eradicated. The Antiguan Racer population took hold and by
2002 the snakes were reproducing. Subsequently the rats were eradicated on
Great Bird Island and the snake population increased by more than 300% over the
rest of the decade (see Murphy, 2010 for more details on this story). This is a
great snake conservation success story, however, to say Alsophis antiguae is
the world's rarest snake is more than a bit misleading, it is just plain wrong.

Some snake species are
notoriously difficult to find. They are often cryptic in color, pattern and
behavior; have the ability to stay hidden underground, underwater, in tree
holes, or other places inaccessible to humans for long periods of time. And,
they are often active only at night when diurnal humans are inactive.

There are many,
many snake species that are known from only a single specimen, making them much
rarer than the Antigua Racer ever was. Thread Snakes of the family
Leptotyphlopidae are poorly known fossorial snakes. McDiarmid et al. (1999)
list 87 species (more species have been described since this volume was
published), 23% of those species listed are known only from their type
localities, which in many cases translates to being known from one, or at most
a few, specimen.

The Dwarf Pipe
Snakes, family Anomochilidae contains three species Anomochilus leonardi, A.
monticola, and A. weberi. A. monticola was described in 2008 on the basis
of two specimens (Das, et al. 2008). The other two species are known from just
a few specimens.

Orlav, et al.
(2009) described the new genus and species Colubroelaps nguyenvansangi from
Lam Dong Province in southern Vietnam. It is a rarely seen, cryptic, dwarf,
fossorial snake combining scale characters both of Colubridae and Elapidae
snakes and is known from a single female specimen. The authors tentatively
placed in the family Colubridae.

Meyer (2003)
noted that South American genus Atractus barely
enters the eastern half of the Isthmus of Panama, where it is extraordinarily
rare and known from five specimens that had been collected over 39 years, the
five Panamanian specimens of Atractus turned out to represent five
species. Meyer described four (A. darienensis, A. hostilitractus,
A. imperfectus, and A. depressiocellus) based upon a single
specimen each. The fifth species A. clarki Dunn and Bailey, was the
second specimen of the species previously known only from the Colombia Chocó.

The Reed Snakes
of the genus Calamaria are small,
ground-soil-leaf litter dwelling snakes of Southeast Asia. Ziegler and Khac
Quyet (2005) described Calamaria thanhi (Family Colubridae) from a
single adult female specimen that was collected in a primary limestone forest
cave. It is the fifth species of Calamaria recorded from Vietnam. Calamaria apraeocularis is known from
only four specimens from Cikora, Sulawesi. Calamaria
boesemani is known from a single specimen from Pinapuan, Sulawesi. A genus
that appears related to Calamaria is Calamorhabdium, it has two species that
are known from a total of four specimens. C.
acuticeps is known from a single specimen from northern Sulawesi (de Lang
and Vogel, 2005).

The Mamberamo
River Water Snake, Heurnia ventromaculata (family Homalopsidae) (top
photo) was described on the basis of a single specimen in 1926 from West Papua,
Indonesia, no other specimens have been found to date. Another homalopsid, Enhydris maculosa, described from a
single specimen in 1879, from Myanmar’s Ayeyarwady River delta, has remained
known from a single specimen for 131 years.

The family
Xenophiidae contains two species: Xenophidion acanthognathus (bottom photo) from Borneo and Xenophidion
schaeferi from peninsular Malaysia. Each are known from a single specimen.
Thus, the entire family of xenophiid snakes is known from two specimens (Lawson
et al. 2004).

William Tanner
described the Autlan Long-tailed Rattlesnake, Crotalus lannomi, from a single specimen collected in Jalisco,
Mexico in 1966. No other specimens have been found. Even, I spent a few days
looking for this snake unsuccessfully. Only recently (Reyes-Velasco et al. 2010)
have five more specimens been collected.

The Rough-scaled
Python, Morelia carinata was
described by L. A. Smith in 1981 from northwestern Western Australia in the
lower sections of the Mitchell and Hunter Rivers, near the coast. Originally
known from just one specimen, others have now been collected, but the number is
far less than that of the Antiguan Racer. The Rough-scaled Python is restricted
to islands of forested habitat in the bottoms of rocky gorges.

Cropani's
Treeboa, Corallus cropani, is known
from only two or three specimens collected in Brazil's highly endangered
Atlantic Coastal Forests. Speculation that it is more terrestrial than the
other treeboas was due to its stouter body and the fact that at least one of
the specimens collected was roadkill. But, the species remains an enigma, with
the Instituto Butantan specimens being lost in the fire that destroyed the facility
this year, it has become even rarer..

These are just a
few examples of snake species known from just one or a few specimens. As
paradoxical as it may seem, the world is full of rare snakes.

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